Thermodynamic machines used for refrigeration, heat production or energy production all refer to an ideal machine called the “Carnot machine”. An ideal Carnot machine requires a heat source and a heat sink at two different temperature levels—it is therefore a “dithermal” machine. It is called a “driving” Carnot machine when it operates by delivering work and a “receiving” Carnot machine (also called a Carnot heat pump) when it operates by consuming work. In driving mode, the heat Qhi is delivered to a working fluid GT from a hot source at the temperature Thi, the heat Qlo is yielded by the working fluid GT to a cold sink at the temperature Tlo and the net work W is delivered by the machine. Conversely, in heat pump mode, the heat Qlo is taken by the working fluid GT to the cold source Tlo, the heat Qhi is yielded by the working fluid to the hot sink at the temperature Thi and the net work W is consumed by the machine.
According to the second law of thermodynamics, the efficiency of a dithermal (driving or receiving) machine, that is to say a real machine whether operating in the Carnot cycle or not, is at most equal to that of the ideal Carnot machine and depends only on the temperatures of the source and of the sink. However, the practical implementation of the Carnot cycle, consisting of two isothermal steps (at temperatures Thi and Tlo) and two reversible adiabatic steps, encounters a number of difficulties that have not been completely solved hitherto. During the cycle, the working fluid may still remain in the gaseous state or it may undergo a liquid/vapor change of state during the isothermal transformations at Thi and Tlo. When a liquid/vapor change of state occurs, the heat transfers between the machine and the environment take place with a higher efficiency than when the working fluid remains in the gaseous state. In the first case and for the same exchanged thermal power levels at the heat source and at the heat sink, the exchange areas are smaller (and therefore less expensive). However, when there is a liquid/vapor change of state, the reversible adiabatic steps consist in compressing and expanding a liquid/vapor two-phase mixture. The techniques of the prior art do not allow two-phase mixtures to be compressed or expanded. According to the current prior art it is not known how to carry out these transformations correctly.
To remedy this problem, it has been envisaged to approximate the Carnot cycle by isentropically compressing a liquid and isentropically expanding a superheated vapor (for a driving cycle) and by compressing the superheated vapor and isenthalpically expanding the liquid (for a receiving cycle). However, such modifications induce irreversibilities in the cycle and very significantly reduce its efficiency, that is to say the efficiency of the motor or the coefficient of performance or the coefficient of amplification of the heat pump.